The pathogenesis of systemic lupus erythematosus (SLE), a prevalent human systemic autoimmune disease, is still unknown. Thus, efforts aimed at understanding disease mechanisms are highly relevant. Because studying humans with SLE is difficult for multiple reasons, we have developed novel genetically lupus-prone NZBxNZW derived congenic NZM lines that are either Stat-4 or Stat-6 deficient. The Stat deficient mice offer unique tools to achieve a better understanding of the role that autoAbs, and cytokines play in the pathogenesis of the disease and may allow dissection of the mechanisms that mediate renal damage in SLE. Backed up by substantial preliminary data, we propose to address the following questions: (1) Is the kidney disease in Stat4 deficient lupus mice dependent or independent of autoAbs? To this end we have produced B-cell deficient NZM2328 mutant mice into which we will restore B cells in the absence of circulating, soluble autoAbs and then cross these mice with Stat4 KO. (2) Is IFN-gamma necessary for the development of autoAbs and target organ disease in Star-deficient NZM mice? This specific aim will test the hypothesis that the absence of IFNgamma may result in early initiation of disease through a failure of regulatory mechanisms in the Stat4-/- mice. To accomplish this we will test directly and systematically the role of IFNgamma at different stages of lupus-like disease development in Stat deficient NZM mice using two different approaches: a) in vivo treatment protocols using IFNgamma and anti-IFNgamma reagents for defined periods of time, and b) a genetic approach in which a conditional expression system for IFNgamma in a tissue-and time-specific manner will be developed. (3) Can we reconstitute the Stat deficient phenotypes in immunodeficient NZM mice? To accomplish this, we will generate NZM2328 completely immunodeficient by introducing a loss of function mutation in both the IL-7R alpha and c-kit receptors that allows hematopoietic reconstitution with any donor strain without requiring administration of pre-transplant conditioning. (4) What are the direct effects of the two Stat4 isoforms on the immune system and on the target organ in NZM2328 lupus mice? For this purpose we will restore Stat4 in T lymphocytes of Stat4 deficient NZM2328 mice by crossing them with Stat4- alpha and Stat4-beta transgenic mice and will study differentially expressed genes in lymphocytes and glomeruli of these lupus mice using micro-array technology. These studies should lead to better understanding of a number of characteristics of SLE and may lead to identification of new targets for therapy.